Conventionally, in this kind of inductive heating device, for example, relating to an inductive cooking device, two switching units are provided, and the conduction ratio of each one is varied, and a low ON voltage power element is used in the switching unit of a longer conduction time, and a high-speed switching power element is used in the switching unit of a shorter conduction time, and thereby the loss is decreased (see, for example, patent document 1).
Further, relating to an inductive cooking device, for example, a plurality of switching elements are connected in parallel, and an IGBT of faster switching speed is used in one switching element, and an MCT of lower ON voltage is used in the other switching element, and the IGBT is operated in turn-off mode, and the MCT is operated in turn-on mode, and thus a technology of reducing the loss is known (see, for example, patent document 2).
FIG. 9 is a circuit diagram showing a conventional inductive cooking device disclosed in patent document 2. FIG. 10 is waveform diagram showing the operation of the circuit of the conventional inductive cooking device disclosed in patent document 2.
As shown in FIG. 9, a control circuit 37 turns on a second switching element 35-b, which is an MCT of low ON voltage power element, for a predetermined time (18 μs). In succession, in 1 μs before the second switching element 35-b is turned off, a first switching element 35-a is turned on for 3 μs, and then the first switching element 35-a is turned off. This operation is repeated, and a load circuit 34 composed of a heating coil 32 and a resonance capacitor 33 is resonated. A high-frequency current is supplied to the heating coil 32, and a high-frequency magnetic field is generated from the heating coil 32. By this high-frequency magnetic field, an electric power is supplied to a pan placed on the heating coil 32.